When Network Coding and Dirty Paper Coding meet in a Cooperative Ad Hoc Network

We develop and analyze new cooperative strategies for ad hoc networks that are more spectrally efficient than classical DF cooperative protocols. Using analog network coding, our strategies preserve the practical half-duplex assumption but relax the orthogonality constraint. The introduction of interference due to non-orthogonality is mitigated thanks to precoding, in particular Dirty Paper coding. Combined with smart power allocation, our cooperation strategies allow to save time and lead to more efficient use of bandwidth and to improved network throughput with respect to classical RDF/PDF.Comment: 7 pages, 7 figure

When network coding and dirty paper coding meet in a cooperative ad hoc network

Abstract — We develop and analyze new cooperative strategies for ad hoc networks that are more spectrally efficient than classical Decode & Forward (DF) protocols. Using analog network coding, our strategies preserve the practical half-duplex assumption but relax the orthogonality constraint. The introduction of interference due to non-orthogonality is mitigated thanks to precoding, in particular Dirty Paper coding. Combined with smart power allocation, our cooperation strategies allow to save time and lead to a more efficient use of the bandwidth and to improved network throughput with respect to classical Repetition-DF and Parallel-DF. Index Terms — Cooperative communications, network coding

Partial network coding with cooperation : a study over multi-hop communications in wireless networks

The imperfections of the propagation channel due to channel fading and the self-generated noise from the RF front-end of the receiver cause errors in the received signal in electronic communication systems. When network coding is applied, more errors occur because of error propagation due to the inexact decoding process. In this dissertation we present a system called Partial Network Coding with Cooperation (PNC-COOP) for wireless ad hoc networks. It is a system which combines opportunistic network coding with decode-and-forward cooperative diversity, in order to reduce this error propagation by trading off some transmission degrees of freedom. PNC-COOP is a decentralized, energy efficient strategy which provides a substantial benefit over opportunistic network coding when transmission power is a concern. The proposed scheme is compared with both opportunistic network coding and conventional multi-hop transmission analytically and through simulation. Using a 3-hop communication scenario, in a 16-node wireless ad hoc network, it is shown that PNC-COOP improves the BER performance by 5 dB compared to opportunistic network coding. On average, it reduces the energy used by each sender node around 10% and reduces the overall transmitted energy of the network by 3.5%. When retransmission is applied, it is shown analytically that PNC-COOP performs well at relatively low to medium SNR while the throughput is comparable to that of opportunistic network coding. The effectiveness of both opportunistic network coding and PNC-COOP depends not only on the amount of network coding but also on other factors that are analyzed and discussed in this dissertation.Keywords: opportunistic network coding, Telecommunications, cooperative diversity, network coding, user cooperatio

Self-concatenated coding for wireless communication systems

In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-ConcatenatedCodes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information withthe SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept.Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits.In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity.Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput

Cancelamento de interferência em sistemas celulares distribuídos

Doutoramento em Engenharia ElectrotécnicaO tema principal desta tese é o problema de cancelamento de interferência para sistemas multi-utilizador, com antenas distribuídas. Como tal, ao iniciar, uma visão geral das principais propriedades de um sistema de antenas distribuídas é apresentada. Esta descrição inclui o estudo analítico do impacto da ligação, dos utilizadores do sistema, a mais antenas distribuídas. Durante essa análise é demonstrado que a propriedade mais importante do sistema para obtenção do ganho máximo, através da ligação de mais antenas de transmissão, é a simetria espacial e que os utilizadores nas fronteiras das células são os mais bene ciados. Tais resultados são comprovados através de simulação. O problema de cancelamento de interferência multi-utilizador é considerado tanto para o caso unidimensional (i.e. sem codi cação) como para o multidimensional (i.e. com codi cação). Para o caso unidimensional um algoritmo de pré-codi cação não-linear é proposto e avaliado, tendo como objectivo a minimização da taxa de erro de bit. Tanto o caso de portadora única como o de multipla-portadora são abordados, bem como o cenário de antenas colocadas e distribuidas. É demonstrado que o esquema proposto pode ser visto como uma extensão do bem conhecido esquema de zeros forçados, cuja desempenho é provado ser um limite inferior para o esquema generalizado. O algoritmo é avaliado, para diferentes cenários, através de simulação, a qual indica desempenho perto do óptimo, com baixa complexidade. Para o caso multi-dimensional um esquema para efectuar "dirty paper coding" binário, tendo como base códigos de dupla camada é proposto. No desenvolvimento deste esquema, a compressão com perdas de informação, é considerada como um subproblema. Resultados de simulação indicam transmissão dedigna proxima do limite de Shannon.This thesis focus on the interference cancellation problem for multiuser distributed antenna systems. As such it starts by giving an overview of the main properties of a distributed antenna system. This overview includes, an analytical investigation of the impact of the connection of additional distributed antennas, to the system users. That analysis shows that the most important system property to reach the maximum gain, with the connection of additional transmit antennas, is spatial symmetry and that the users at the cell borders are the most bene ted. The multiuser interference problem has been considered for both the one dimensional (i.e. without coding) and multidimensional (i.e. with coding) cases. In the unidimensional case, we propose and evaluate a nonlinear precoding algorithm for the minimization of the bit-error-rate, of a multiuser MIMO system. Both the single-carrier and multi-carrier cases are tackled as well as the co-located and distributed scenarios. It is demonstrated that the proposed scheme can be viewed as an extension of the well-known zero-forcing, whose performance is proven to be a lower bound for the generalized scheme. The algorithm was validated extensively through numerical simulations, which indicate a performance close to the optimal, with reduced complexity. For the multi-dimensional case, a binary dirty paper coding scheme, base on bilayer codes, is proposed. In the development of this scheme, we consider the lossy compression of a binary source as a sub-problem. Simulation results indicate reliable transmission close to the Shannon limit